fix vinegar example

Author: alex-courtis

doc/nvim-tree-lua.txt

@@ -1092,7 +1092,7 @@ You can easily implement a toggle using this too:
       local view = require"nvim-tree.view"
       local api = require"nvim-tree.api"
       if view.is_visible() then
-        api.close()
+        api.tree.close()
       else
         require"nvim-tree".open_replacing_current_buffer()
       end